Roller for pulverizing mills



Oct. 2, 1956 w. A. SPEER ROLLER FOR PULVERIZING MILLS Filed Dec. 13, 1954 INVENTOR. WH.L.|AM A. fJpEEQ.

ATTORNEYS United States Patent ROLLER FOR PULVERIZING MILLS William A. Speer, Charleston, S. C.

Application December 13, 1954, Serial No. 474,746

3 Claims. (Cl. 241129) This invention relates to restoring rollers of a pulverizing mill such as the type from which material, when ground to suflicient fineness, is removed by an air lift and wherein pendant rollers are provided which are revolved at a high speed within and in contact with the inner peripheral surface of a grinding ring or bull ring between which and the rollers the material is reduced. A mill of this character is disclosed in U. S. Patent No. 1,582,538, issued to Fred I. Raymond on April 27, 1926.

In pulverizing mills of the character described, the abrasive action of the material being ground between the revolving pendant rollers and encircling bull ring causes gradual decomposition of the outer peripheries of the rollers and the inner periphery of the bull ring to ultimately form a broad groove in the periphery of each of the rollers and in the inner face of the bull ring. This gradually reduces the grinding efliciency of the mill to such an extent that it has been necessary heretofore to at least replace the worn rollers with new rollers or to replace both the worn rollers and the Worn bull ring with new rollers and a new bull ring.

Such rollers and bull rings are usually cast from a nickel steel alloy properly heat-treated, with the result that the rollers and bull rings are not only expensive to produce or purchase, but it is also an extremely expensive operation to remove a worn bull ring from a pulverizing mill of the character described and to replace the same with a new bull ring, notwithstanding the fact that it is then necessary to stop the pulverizing mill for a substantial period of time during the replacing of a bull ring with a new bull ring.

It is therefore an object of this invention to provide novel pulverizing rollers for a pulverizing mill which will at least quadruple the useful life of a bull ring without the necessity of removing the worn bull ring from the pulverizing mill, and which will at least double the useful life of each of the pendant rollers of a pulverizing mill before it is necessary that they be discarded and replaced with new rollers.

To this end, the rollers of a pulverizing mill are provided with a peripheral surface having a contour corresponding to the contour of the depression or recess previously formed in the inner or grinding face of the corresponding bull ring as a result of the abrasive action of the material being ground between the rollers and the bull ring.

It is more specifically an object of this invention to provide a novel pulverizing roller to cooperate with a bull ring having a broad flat-bottomed groove therein wherein each roller is provided with a broad flat projection thereon which fits in said groove, thus providing more eflicient co-acting grinding surfaces on the rollers and bull ring than have been present on those used in pulverizing mills heretofore.

Some of the objects of the invention having been stated, other objects will appear as the description proceeds, when taken in connection with the accompanying drawings, in which-- r CE Figure 1 is a vertical sectional view of a pulverizing mill of the centrifugal type showing the condition of the rollers and bull ring before they have become worn;

Figure 2 is a sectional plan view taken substantially along line 22 in Figure 1;

Figure 3 is a greatly enlarged fragmentary vertical sectional view of the area defined in broken lines and indicated at 3 in Figure 1;

Figure 4 is a fragmentary view similar to Figure 3, but showing the condition of the portion of one of the pulverizing rollers and the inner periphery of the bull ring after they have become worn to where their efficiency is so impaired as to render them useless in their present condition;

Figure 5 is a view similar to Figure 4 showing how the periphery of each roller is shaped to conform to the inner surface of the bull ring so the rollers and the bull ring can be re-used without removing the bull ring from the pulverizing mill.

In order that the restoration of the rollers of a pulverizing mill may be clearly understood, a brief description will first be given of one .type of centrifugal pulverizing mill having rollers therein of the character to which the invention is applied. The pulverizing mill is shown as being of a type disclosed in said Raymond Patent No. 1,582,538, although the invention is not particularly limited to rollers used only on this type of pulverizing mill.

Referring to Figure 1, the numeral 10 broadly desig nates the main housing or casing of the mill having a base plate 11 thereon which is shown as supported on a foundation 12. An upper or auxiliary housing 13 is removably secured on the main housing 10, as by bolts or screws 14. A shaft 15 extends vertically through the center of the main casing 10 and upwardly into the auxiliary or upper housing or casing 13.

The lower end of the vertical shaft 15, outside of the main housing 10, has a bevel gear 16 fixed thereon driven by a bevel pinion 17 on a driving shaft 20. It will be observed that the lower portion of shaft 15 is journaled in a bearing 21 carried by or integral with the main housing 10. For purposes of clarity, the bearing for supporting the upper part of the shaft 15 is omitted.

A spider 24 is fixed on the upper end of shaft 15 and a pluralityof roller journals 25 are pivotally connected to the spider 24, as at 26. Each of the journals 25 has a substantially vertically extending roller shaft 27 journaled therein, the lower end of each of which has a pulverizing roller 30 fixed thereon, there being four of the pulverizing rollers 30 shown in Figure 2. The pulverizing rollers 30 are adapted to bear, through centrifugal force, against the inner periphery of a grinding ring or bull ring 31 fixed to an inwardly projecting rib 32 on the wall of the main housing or casing 10 of the pulverizing mill.

An annular bottom plate 33 forms a grinding chamber 33a in the main housing 10 and is provided with a central opening 34 for admission of air to the mill from air intake duct 35. As disclosed in said patent, the pulverizing mill is provided with a deflecting plate 37 secured to a spider 40 fixed to shaft 15. The spider 37 has a plurality of circularly spaced angularly disposed plows or scoops :3 fixed thereon whose lower ends work close to the annular bottom plate 33 and whose upper ends extend upwardly through respective openings formed in the periphery of the deflecting plate 377 The upper ends of the plows 43 are arranged so as to deliver the material scooped up from the plate 33 into the spaces between the rollers 30 and bull ring or grinding ring 31 in advance of the rollers 30. The diameter of the deflecting plate 37 is substantially the same as the interior diameter 0 the bull ring 31.

Suitable means may be provided for feeding aggregate material, such as phosphate, lime and limestone into the pulverizing mill and, in this instance, a rotary feeder '47 is provided in a feeding hopper 50. It is thus seen that, in operation, material is fed into the mill by the feeder 47, falls downwardly through the mill and is carried around centrifugally by rotation of the pulverizing rollers 30 and the structure on which they are supported. The material is then pulverized between the rollers 34) and the bull ring 31.

Air is introduced into the bottom of the mill through the duct 35 and air intake opening 34 and the air passes upwardly through the openings 44, upwardly and inwardly in an angular stream past the plate 37 in chamber 33a and through the stream of material falling from the bull ring 31.

Thus, the finer particles are, in a large measure, picked up by the air currents and the material flows and is carried off by the air current which finds its exit from the mill at 51 through the upper or auxiliary housing 13. The remaining material, including the heavy particles, which have not been sufficiently ground, falls upon the deflecting plate 37 and some of the material spills over the edge of the plate 37 and is subjected again to the separating action .of the air current, while the rest of it passes backwardly into the plow openings 44 where it is given a second air separation which carries the lighter particles out of the mill. The heavy particles in the bottom of chamber 33a are scooped up by the plows 43 and, with the heavy particles falling onto plate 37 or carried .into the plow openings, are delivered to the grinding ring in advance of the several rollers 30.

The rollers 30 are usually made from a nickel steel alloy properly heat-treated to harden the same or they are cast from a grey iron and are provided with a superficially hardened surface. As best shown in Figure 3, when new rollers 3b and a new bull ring 31 are originally installed, the bull ring 31 has a flat inner periphery or grinding surface 314: thereon and each of the pulverizing rollers 39, which usually is of greater vertical dimension than the vertical dimension of the bull ring 31, has a slightly rounded or convex peripheral surface 30a which is blended into the upper and lower surfaces of the corresponding pulverizing roller 39 by relatively small rounded edges 3% each having a relatively small radius.

Now, due to the abrasive action of the material being pulverized between the rollers 39 and a bull ring 31, it has'been found that, when using the nickel alloysteel'type of .pulverizing rollers, the proximal or mating surfaces of the rollers 39 and bull ring 31 become worn to Where, in a period of approximately two thousand hours of usage, which is equivalent to approximately six months of usage, sixteen hours a day, five days a week, the proximal surfaces of the rollers and the bull ring 31 appear as shown in Figure 4 wherein it will be observed that the periphery of each roller 3% has a fiat-bottomed groove Silc extending substantially throughout the width of the periphery thereof and which defines a pair of rounded ridges or projections 380! on opposite sides or on the upper and lower edges of each of the pulverizing rollers 30. It will also be noted that the bull ring 31, as shown in Figure 4, has a relatively broad fiat-bottomed groove 31]) on the inner face or periphery thereof forming inwardly projecting ridges 310 on the upper and lower edges of the bull ring 31 at the inner surface thereof.

Heretofore, when the rollers and bull ring have become worn substantially as shown in Figure 4, it has been neces sary to remove the upper or auxiliary housing 30 from the pulverizing mill as well as many other parts thereof secured to the main housing It and then replace the worn rollers 39 on the shafts 27 with new rollers. It has also been necessary to remove the worn bull ring from the main housing 1i? and replace the same with a new bull ring. it is a time consuming and expensive task to cany out the various operations necessary to replace a worn bull ring with a new bull ring and to replace the worn rollers 30 with new rollers, and the rollers 30 and bull ring 31 are, in themselves, extremely expensive to produce or purchase.

In order to obviate the necessity of replacing the bull ring 31 with a new bull ring each time that it is normally necessary to replace the pulverizing rollers, and to also greatly increase the useful life of the pulverizing rollers 30 and the bull ring 31 and .to thereby reduce the cost of maintaining the pulverizing mill by approximately onefourth the usual cost of maintaining such mills, the worn pulverizing rollers 3% are reshaped to mate with the bull ring which permits using a set of rollers over again without the necessity of replacing the bull ring 31 or reworking the bull ring 31 inany way whatsoever.

To this end, the periphery of each roller is reshaped into the configuration shown in Figure 5 by first removing the,

pulverizing rollers 30 from the pulverizing mill and refinishing or grinding the peripheral surfaces thereof to form a projection or ridge on the periphery thereof having a broad flat outermost surface 30:: thereon which projection is rounded at its upper and lower edges, as at 30f to thereby form a peripheral Surface on each of the pulverizing rollers 34) which conforms substantially to'the flat bottomed groove 31b previously formed on the inner surface of the bull ring by the natural abrasive action of the material being pulverized between the rollers 3 0and the bull ring 31. In normal grinding position, the rollers by being disposed on vertical axes present with the 'bull ring a substantially uniform clearance throughout the vertical extent of their broad flat projections. If so desired, the recessed remote peripheral edges of each pulverizing roller 30 may also be rounded slightly asatfitlg to assist in deflecting the material to be pulverized between the rollers Stl .and the bull ring 31. As a further step, the periphery of each roller 30 may be superficially hardened by suitable heat treatment to further lengthen the useful life of the rollers 31 It should be noted that the upper and lower edges of the broad fiat outermost surface we on the projection or ridge on the periphery of the pulverizing roller 30 are spaced from the upper and lower surfacesof thepulveri zing roller 39; that is, the broad flat outermost surface 30; is of lesser width or height than the roller 30 per ,Se and is substantially centrally located between the upper and lower surfaces of the roller 30 per se in order to provide convex top and bottom shoulders 3% on the roller 30 which are disposed inwardly relative to the broad flat surface Sile.

It should be noted that the inner surface of the bull ring 31 assumes substantially the form shown in Figures 4 and 5 when it has become worn and that the shoulders 3% on the improved pulverizing roller 30 approach the inwardly projecting annular ridges 31c on the upperand lower edges of the bull ring 31. v

The rollers normally wear faster than the ring because of the small diameter of the rollers compared with .the diameter of the bull ring. Thus, it is apparent that several sets of rollers 31) may be used in succession ,without replacing the bull ring 31 with a new one.

It should also be noted that the present invention results in a novel form of bull ring and novel pulverizing rollers having greater working surfaces thereon as compared to the form shown in Figure 3, as exemplified in the broad fiat bottomed groove 31b having relatively small concave surfaces at its junctures with the ridges 31c at opposite edges of the bull ring 31 and, also, as exemplified by the projection having a relatively broad flat .surface 362 and small rounded corners 30 and the shoulders 3911 on the periphery of each of the pulverizing rollers 39. Of course, each time that the rollers 30 become worn in the manner shown in Figure .4, it is apparent that they may be reshaped and thus reused several times before it is necessary to discard the pulverizing rollers 30.

It is thus seen that I have provided improved pulverizing rollers for a pulverizing mill to conform to the recessed inner periphery of the bull ring, thereby greatly reducing the cost of maintaining and operating a pulverizing mill over relatively long periods of time as compared to the cost of operating and maintaining puiverizing mills heretofore and also substantially multiplying the useful life of existing pulverizing rollers and bull rings.

In the drawings and specification there has been set forth a preferred embodiment of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined in the claims.

1 claim:

1. In a pulverizing mill of the centrifugal type having a bull ring, said bull ring having a pair of axially opposed inwardly projecting ridges at its top and bottom and a broad flat peripheral groove therebetween in the inner face of the ring, improved pulverizing rollers for centrifugally engaging the inner surface of said bull ring, each roller having a broad fiat peripheral outermost projection thereon of substantially the same Width as the width of said groove in the bull ring, said rollers in their normal grinding position presenting With the bull ring a substantially uniform clearance throughout the vertical extent of their said broad fiat projections, axially opposed top and bottom shoulders on opposite sides of each of said broad fiat projections and of lesser diameter than the broad fiat projection and being adapted to approach said ridges on the bull ring.

6 2. A roller according to claim 1 wherein opposite end edges of said projection are convex.

3. A roller according to claim 1 wherein. said shoulders are curved and recede away at increasing distances from the ridges of the bull ring.

References Cited in the file of this patent UNITED STATES PATENTS 61,599 Bear Ian. 29, 1867 99,205 Johnston Jan. 25, 1870 287,653 Fish Oct. 30, 1883 303,125 Corcoran Aug. 5, 1884 589,036 Seymour Aug. 31, 1897 872,201 Rudnick Nov. 26, 1907 1,027,222 Sturtevant Mar. 21, 1912 1,358,739 Herbst Nov. 16, 1920 1,605,050 McNinch ilov. 2, 1926 1,884,104 Moore Oct. 25, 1932 1,898,823 Forbes Feb. 21, 1933 2,335,411 Hellmanns Nov. 30, 1943 2,532,092 Frangquist Nov. 28, 1950 2,551,946 Haug May 8, 1951 2,698,142 Crites Dec. 28, 1954 FOREIGN PATENTS 123,259 Great Britain Feb. 20, 1919 153,751 Great Britain Nov. 18, 1920 346,428 Great Britain Apr. 7, 1931 

